1. Field of the Invention
This invention relates to a mandrel for supporting a stent and a method of applying a coating to the stent supported by the mandrel.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
FIG. 1 illustrates a conventional stent 10 formed from a plurality of struts 12. The plurality of struts 12 are radially expandable and interconnected by connecting elements 14 that are disposed between adjacent struts 12, leaving lateral openings or gaps 16 between adjacent struts 12. Struts 12 and connecting elements 14 define a tubular stent body having an outer, tissue-contacting surface and an inner surface.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent strut surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
A shortcoming of the above-described method of medicating a stent is the potential for coating defects. While some coating defects can be minimized by adjusting the coating parameters, other defects occur due to the nature of the interface between the stent and the apparatus on which the stent is supported during the coating process. A high degree of surface contact between the stent and the supporting apparatus can provide regions in which the liquid composition can flow, wick, and collect as the composition is applied. As the solvent evaporates, the excess composition hardens to form excess coating at and around the contact points between the stent and the supporting apparatus. Upon the removal of the coated stent from the supporting apparatus, the excess coating may stick to the apparatus, thereby removing some of the needed coating from the stent and leaving bare areas. Alternatively, the excess coating may stick to the stent, thereby leaving excess coating as clumps or pools on the struts or webbing between the struts.
Thus, it is desirable to minimize the interface between the stent and the apparatus supporting the stent during the coating process to minimize coating defects. Accordingly, the present invention provides for a device for supporting a stent during the coating application process. The invention also provides for a method of coating the stent supported by the device.
The present invention provides a mandrel for supporting a stent. The mandrel includes a body for extending at least partially into a hollow stent for supporting the stent during the process of coating the stent. The body has a first section of a first size and a second section of a second size, the second size being greater than the first size. The body can be attached to a motor for providing rotational motion.
In one embodiment, the first section is longer than the second section. In another embodiment, the first section does not make contact with the inner surface of the stent. In still another embodiment, the second size includes a diameter that is less than the inner diameter of the stent.
Also provided is a device for supporting a stent. The device includes a mandrel capable of extending at least partially through a hollow body of a stent and a gear supported by the mandrel for rotating the stent during the process of coating the stent. The gear can include teeth. The gear can also include a textured or roughened surface.
In one embodiment, the positioning of the gear on the mandrel can be adjusted. In another embodiment, the diameter of the gear is greater than the diameter of the mandrel, and the diameter of the gear is less than the inner diameter of the stent. Accordingly, the outer surface of the mandrel does not contact the inner surface of the stent.
The present invention also provides a method of coating a stent. The method includes positioning a stent on a mandrel having a gear member. The method additionally includes rotating the mandrel to cause the gear member to provide rotational motion to the stent and applying a coating material to the stent. In one embodiment, the act of applying includes spraying a composition including a polymer added to a fluid and optionally an active agent added thereto onto the stent.